This invention broadly relates to a thermal stamping device for transferring a film from a carrier web to the surface an object and more particularly to a thermal stamping device capable of continuously and uniformly applying a film despite variations in the width of the surface to which the film is applied.
Thermal of hot stamping devices are known for continuously transferring a film from a carrier web to the outer surface of an object by utilizing a heated transfer roll which presses the film against the object while simultaneously activating a heat sensitive adhesive capable of attaching the film to the surface.
Uniform transfer of the film requires that the transfer roll traverse the object at a constant transfer pressure and speed. Prior art thermal stamping devices are known, such as disclosed by the inventor of the present application in Japanese patent publication No. 9124/78, which include a pressure control system for detecting and maintaining a constant total transfer pressure; a speed control system for detecting and maintaining a constant transfer speed; and an automatic arrangement for eliminating any detected deviation from the reference transfer pressure and speed.
One disadvantage of this prior art device is the inability to vary either the total transfer pressure or the transfer speed with respect to changes in the actual width of the surface to which the film is applied. Since the pressure control system of the above-noted prior art device is directed to controlling the entire transfer pressure imposed by the transfer roll on the whole width of the object to be stamped, the system is incapable of controlling the transfer pressure per unit width actually stamped.
This drawback causes problems when stamping a product like that illustrated in FIGS. 1 and 3 where a surface PS of an object G is provided with windows R1, R2, and R3. If the entire surface PS of the object G is stamped with a film transferred from a carrier web, it can be seen that the actual transfer width for distances I, III and V is equal to the entire width W of the object G, whereas the actual transfer width for distance II is (W-a) where a is the width of window R.sub.1, and the actual transfer width for distance IV is (W-b-c) where b equals the width of window R.sub.2 and c equals the width of window R.sub.3. If the entire transfer pressure required for uniform stamping is calculated for distances I, III and V and used as the reference pressure, the transfer pressure per unit width actually stamped for distances II and IV becomes excessive resulting in the non-uniform transfer of the film. On the other hand, if the transfer pressure required for distances II or IV is calculated and utilized as the reference pressure, the transfer pressure per unit width actually stamped for distances I, III and V becomes insufficient for uniform stamping.